Dynamical mean-feld theory (DMFT) studies frequently observe a new structure in the local spectral function of the SU(2) Fermi-Hubbard model (i.e., one-band Hubbard model) at half _lling: In the metallic phase close to the Mott transition, subpeaks emerge at the inner edges of the Hubbard bands.

Here we demonstrate that these subpeaks originate from the low-energy e_ective interaction of doublon-holon pairs, by investigating how the correlation functions of doublon and holon operators contribute to the subpeaks [1, 2]. We use the numerical renormalization group (NRG) as a DMFT impurity solver to obtain the correlation functions on the real-frequency axis with improved spectral resolution [3]. A mean-_eld analysis of the low-energy e_ective Hamiltonian [2] provides results consistent with the numerical result.

The subpeaks are associated with a distinctive dispersion that is di_erent from those for quasiparticles and the Hubbard bands. Also, the subpeaks become more pronounced in the SU(N) Hubbard models for larger number N of particle avors, due to the increased degeneracy of doublon-holon pair excitations. Hence we expect that the sub-peaks can be observed in the photoemission spectroscopy experiments of multi-band materials or in the ultracold atom simulation of the SU(N) Hubbard models.